1. Field of the Invention
The present invention relates to a process control system for metal-depositing baths, which system serves to monitor the chemical composition of a bath liquid and which, in the event of deviations of individual components of the bath liquid from a theoretical value, regenerates the bath liquid by supplying correcting liquid to the bath, and more particularly to such a system which comprises an automatically operating analyzer which is connected to a measured value adjusting device which, in dependence upon the established difference between a "reference" value and an "actual" value of the bath liquid component which is subject to analysis, controls the supply of the correcting liquid to the bath.
2. Description of the Prior Art
In order to carry out titration, or to determine the chemical state of a galvanic bath, and in order to regenerate the bath liquid of a galvanic bath, it is known in the art to automatically withdraw a given quantity of liquid from the bath at predetermined times within a cycle. This is effected with the aid of a process control system containing a clock. This quantity is supplied with a reagent in portions and automatically. The time taken until the point of change occurs is represented as an "actual" section value and is compared with a "reference" section value. The difference established between these section values is a control value which governs the automatic supply of correcting liquid to the bath.
Fully automatically operating analysis devices are also well known in the art. In such devices, the samples which are to be analyzed are mixed by means of suitable diluting and/or reaction agents and are subsequently colorimetrically measured. The analyzer is set up in such a manner that following the analysis of a specimen, its flow supply lines are cleansed and automatically dried before the analysis of the next sample is initiated. A process control unit, e.g. a program card or a program tape, governs the function and the control of the analyzer automatically. For example, water, methanol or acetic acid is used to cleanse the analyzer. The analyzer is set up in such a manner that the liquid which is to be analyzed can be analyzed into a plurality of components, i.e. in its constituents.
Also known is a control device which automatically maintains constant the composition of an electrolytic bath and by means of which the additives to the electrolyte in the bath are effected in the correct quantities under the control of a pump. In dependence upon the quantity of electricity flowing in the electrolytic bath, correcting liquid is supplied to the bath at predetermined times by means of an adjustable number of piston strokes.
The previously known processes, process control units and devices serving to maintain constant the chemical composition of the liquid in galvanic baths, served the function of monitoring and analyzing the bath liquid of a specific galvanic bath, and in dependence upon the result of the analysis and also in dependence upon the particular current load of the bath, of adding a specific quantity of the relevant correcting liquid to the bath for its regeneration. If, for example, a plurality of galvanic baths of different types are involved in one plant, e.g. baths for coating electric components with noble metals, with copper and/or for the contour etching of components, i.e. galvanic baths whose bath liquids have differing chemical compositions, it is necessary to provide special analysis devices for these baths. The analysis and possibly also the regeneration of a galvanic gold bath is of particular importance, as these baths also contain so-called alloy metals which impart special mechanical properties to the gold layer. The analysis of cyanide gold baths, which in addition to quantities of alloys, also contain buffer substances and possibly also organic additives, is extremely expensive. To establish the gold in potassium aurocyanide, a photo-metric process is employed, utilizing a commercially available reagent (astra-violet). The analysis must extend to all of the basic bath components, and therefore is also time consuming. In such baths, the gold content generally amounts of 9 to 10 g/1, but can also be less, and, for example, amount to only 1 g/1. However, when such a bath is in a plant, the gold content can only be maintained constant with great difficulty, because of the long duration of the analysis process which, in the case of these baths, has previously been carried out only manually, and because of the additional time required to regenerate the individual baths. Therefore, considerable deviations from the reference value of the gold content cannot be ruled out. Too high or too low of a gold content affects the thickness of the produced coating layers and also indirectly affects the consumption of noble metal and the quality of the coating layer. Therefore, in order to adhere to the theoretical or reference value, it is necessary to repeat the analysis of such baths at intervals which occur as frequently as possible. If a plurality of similar to unsimilar baths are involved, as described above, in galvanic plants it is desirable that the monitoring of the individual baths should take place with the least possible number of personnel, and also with a low technical expense.